Moving onwards and upwards....

Well,

Following on from my last post, I've been making some more bits and bobs to go with the SSB exciter:

http://g0mgx.blogspot.co.uk/2014/06/history-repeating.html

I've made the Triple Balanced Mixer:

As is becoming an apparent recurring theme, my isolation between the different ports isn't measuring as good as the author, however I can measure LO-RF and LO-IF isolation of about 40dB and more like 50dB of RF-IF isolation; which isn't at all bad.

The mixer uses 5 bifilar wound inductors, each of 12 turns on a FT37-43 and two well matched sets of diodes.

I have then added the post mixer amplifier and constructed the first of many band pass filters. This one is for 40M or 7.0 - 7.2 MHz.

Information on the filters is here:

http://homepage.tinet.ie/~ei9gq/bpf.html

which includes a link to a spreadsheet credited to John Charlton G3VRF which is an excellent calculator tool.

When I first built this filter is was too low in frequency (the yellow trace below) so I reduced the inductors by one turn each to get the purple trace. The markers are at 7.0MHz and 7.2MHz:

So the filter, at least, is now looking rather good.

I've had another good look at the exciter from last time but still I can't see why my output level is so much lower than the authors; will have to look again tomorrow!

Good, egh?

Bench Sig Gen - Any bright ideas?

Well,

Been fiddling around at home today and building a bench RF Signal Generator. I have a homebrew one already but it's a bit hit and miss to tune, I also have an old Avo valve based signal generator, but that's extremely heavy, very large and generates lots of heat!

I saw a schematic for a suitable bench Signal Generator a while ago in Experimental Methods in RF Design (page 7.15 Fig 7.27), so I thought I would have a go at making one.

Here's what it looks like in it's current state of construction:

The tuning capacitor on the RHS is the main tuning and the second variable capacitor on the LHS is the fine tuning; that should help make it easier to set the device.

The toroid you can see nearest the front of the picture above is a little odd; the secondary is just a single turn which in reality is the leg of the diode you can see just passing through the centre.

I then found in my box labeled "projects" a digital dial kit from QRP kits:

http://www.qrpkits.com/freqcounter.html

I've used these in projects in the past and I must have ordered an extra one some time ago, anyhow as this is a surface mount project, it was extreme soldering time again. If anyone doesn't realise how small these components are, here's one of the resistors on my thumb nail:

So, here is the underside of the project board completed:

And the display side:

Ideally you would calibrate this with as high a frequency as possible, but I have used my 10MHz frequency standard from here:

http://g0mgx.blogspot.co.uk/2011/07/ocxo-oh-you-mean-ocxo.html

And here is the counter connected to the signal generator, I've added an additional buffer output stage between the output PAD and the counter in my build:

So, the output of the new bench Signal Generator looks quite good, here's some shots of the device set at 10MHz exactly:

This now needs a case, but I am going to wait until the end of the month when I will be at the National Hamfest and see if I can find anything there. I'm away between now and then in A71 land so it will just have to wait.

There is an expression about curiosity and cats:

Good though, egh?

Where does it lead? A bridge to nowhere!

Well,

Following my initial attempts at making a Return Loss Bridge (RLB) last time:

http://g0mgx.blogspot.co.uk/2013/09/return-loss-bridge-where-does-it-lead.html

I've taken some advice; the most common suggestion was that my construction was too slap dash! Could do better and must try harder - reminds me of my school reports!

Here's a remade version of the RLB in quite high-res:

Now this is much neater, however, the basic problem is going to be (so I'm being told) that the wires and the box create a feedline - my construction makes that feedline a load of pants....

Now, I then tried to make an alternative RLB using more normal type of construction techniques:

And that has a slightly worse directivity reading to the one in the box!

So, then I followed another suggestion and constructed an RLB using SMD resistors and this one looks like this:

The observant amongst you will see that the resistors are in fact 52R3 (thats 52 point 3 ohms); these were left over from the power meter project back here:

http://g0mgx.blogspot.co.uk/2012/11/the-power-is-with-me.html

This newly made RLB when boxed measures at 26.3 dB directivity - so this is an improvement and much closer to my target value of 30 dB.

I then decided to rummage further and I found some 100R SMD resistors, and made a third (forth?) RLB using 2 100R resistors in parallel for each 50R theoretical component:

Now this version of the RLB measures as 23dB directivity - so just the same as the first one! Bah - I'll stick with the version containing the 52R3 components for now....

New ham cat's not been helping much:

Fun, egh?

Return Loss Bridge - Where does it lead?

Well,

More fiddling today and I have been making a return loss bridge to help with my "RF Workbench" measurements.

A RLB (Return Loss Bridge) is a device that will help me understand how close to a desired target impedance of 50R things are. And by things I mean kind of anything really, an amplifier, a dummy load, an antenna, a rubber plant - anything. That last item isn't necessarily true - I am just checking you are paying attention.

What a RLB does is allow you to measure the difference between the input power and the power reflected as a result of an impedance miss-match. So the higher the return loss the better the impedance match (unlike SWR where lower numbers indicate a better match).

Here's a simple schematic of an RLB that I have stolen:

So, I've made mine using 2 x 100R resistors in parallel for each of R1, R2 and R3 and the transformer T is wound with 10 turns bifilar on a FT37-43:

Now, to calculate the bridge directivity, firstly you would connect a 50R output signal generator at the test frequency to the "RF" port and a 50R terminated 'scope at the "Detector" port. Once this is set up we need to measure the peak-to-peak voltage reading on the 'scope. In my case I set this up for 7MHz and read a value of 57 mV with the "?" port open circuit. If I now connect a 50R load to the "?" port and take the reading again, I get a value of 3.7 mV. This tells me that the directivity of the bridge is:

20 LOG (57 / 3.7) = 23 dB (ish)

Now, that's a bit pants! I was hoping for at least 30dB. THe first thing I tried was changing the toroid in the transformer "T" - I remade it using a FT37-50 with 10 bifilar turns:

This change hasn't made any difference at all!

The theory of operation is that you would set your signal generator to the frequency required and then first measure the detector reading with the "?" port open and then repeat the measurement with the device under test connected to the "?" port like this:

But given that my RLB only has a directivity of 23 dB ish I think I need to make some improvements. This should turn out to be a useful addition to the shack however, and in my quest to learn more and more about RF measurement, impedance and the like - this has been a good experiment!

Odd, Egh?

A Pixie - Really?

Well,

Been fiddling recently with some very basic CW transceiver designs, most notably the classic QRP "Pixie" design.

This is a very basic CW transceiver comprising a Colpitts oscillator, a second stage which is an RF Amp in TX and a mixer in RX plus an Audio Amp. The basic schematic looks something like this:

I stole the image above from The free information Society:

http://www.freeinfosociety.com/electronics/schemview.php?id=1943

I've substituted the MPSH10 transistor in mine, but apart from that it's going to be the same circuit except for a different band.

To build one of these for a different band, it should be a case of changing the crystal frequency and also the output filter.I'd like to make one of these for the CW end of 20M; this led me to do some investigation into Low Pass output filters. Starting in the most excellent reference book Experimental Methods in RF Design, we can design a very simple Low Pass Filter like this:

Having constructed the filter above, it was clear that the roll off wasn't very sharp, so I did the maths for a 5 pole filter (above is a 3 pole). Here's the 5 poll filter constructed in a very experimental way:

I've hooked one side of the filter up to the Tracking Generator in the Spectrum Analyser and the other to the Analyser input, here's what I see:

Which means that when the basic oscillator in the Pixie is connected to this filter as its output low pass, we get this suppression of the output harmonics:

Which all looks rather good to me!

As an alternative to the "norm", here's a picture of Saki dog:

Fun, egh?

This week I'm 9H3JM - that means I am in Malta!

Well,

Finally I have some time off work and have taken a trip to the island of Malta for a holiday with my Wife.

I brought my FT-817, a PSU, buddipole and a laptop with me (and yes, I got stopped at customs AGAIN):

Getting a license for Malta was really easy. I already hold a HAREC - that's a Harmonised Amateur Radio Examination Certificate which means that I qualify for a license in CEPT countries without sitting the local qualification. I simply filled out a form, sent it off with copies of appropriate bits of paper and the license fell through the front door a couple of weeks later.

It's rather nice here, and have had an hour or so today playing radio:

I don't expect to work the world with my 5 watts of RF out of the FT-817, but it sure is fun. I am on EU-023 (I think) after all! Only running JT-65 ad PSK-31 but getting out well considering the limited nature of the station.

Fun, egh?

Can we do it with Less - Part II

Well,

Following my musings last time about how far not much RF can travel, I took another look at the site of W3PM here:

http://www.knology.net/~gmarcus/

This is where I found the inspiration for my WSPR beacon back here:

http://g0mgx.blogspot.co.uk/2012/05/back-to-real-homebrewing.html

So I took a look at the latest software for the project - noting that my callsign appears in the credits! - then just reprogrammed my project with the latest code after changing the appropriate bits like callsign and locator et cetera.

I then calibrated the output for an accurate 100mW - I also calculated the loss in the coax between the output and the antenna - I make that about 1dB.

So, I have 100mW or 20bBm out of the box, 1dB loss in the coax = 19dBm or about 80mW into the antenna.

Remembering that propagation conditions are quite poor at the moment, here are the results of an overnight run:

Simply stunning, egh?

Can we do it with less?

Well,

My 30M QRSS Arduino based beacon is still on the air; and I am receiving reports via e-mail from time to time. The most recent was from Andre, DL8WX; he is in JO30WE 716.75 km (445.390 miles), bearing 112.3 degrees from me and said "I found ur beacon last night with a strong signal on 10140.02 kHz for the first time!". The beacon project build is here:

http://g0mgx.blogspot.co.uk/2013/06/qrssing-again.html

Last night, I left my FT-DX-3000 WSPRing on 40M using the dipole I made here:

http://g0mgx.blogspot.co.uk/2013/04/well-further-to-my-musings-last-time.html

and here's the result:

Before I left it alone I measured the power out exactly using my Arduino based power meter from here:

http://g0mgx.blogspot.co.uk/2012/11/the-power-is-with-me.html

and the list of stations heard/hearing looks like this:

So, you have to wonder, if this is achievable with 40dbM (10dBW or 10 watts), what could we achieve with far less power?

Given that the most recent 50mW QRSS beacon project is Arduino based, I could write some software to generate WSPR using that, I would need a GPS to give me an accurate time source, there's also exactly that in a (not quite finished) project from here:

http://g0mgx.blogspot.co.uk/2012/05/more-wspring-and-qrssing.html

or even this Hans Summers project from here will do it exactly as I describe above (GPS and WSPR):

http://g0mgx.blogspot.co.uk/2012/07/qrssing-again.html

So, time to fiddle!

As a slight aside, I'm going to Malta for a week soon and I have 9H3JM for use there; as my FT-450 is in Doha I have bought myself an FT-817 to take with me. This radio is capable of outputting much lower power levels than the other radios I have here, so perhaps the easiest option for some really low power WSPR is to use that?

Lets see.

I Never Fail to be Amazed

Well,

Just been rummaging through recent email in my inbox and a digest from the QRSS Knights has caught my eye. There are a set of reports from Joze, S52AB who is in locator JN75ou.

Here's the image that one of his reports are based on (Joze has done the annotation, not me):

So the distance from IO93ga (me) to JN75ou (him) is 1439.44 km or 894.470 miles at a bearing of 116.9 degrees, so my 50mW is making it all the way to Slovenia.

Would you Adam and Eve it?

QRSSing Again, Again

Well,

Been fiddling a little more here, and stuck the Arduino QRSS beacon inside a box - it's currently being powered by an old bench PSU that I made many years ago - this PSU has a really nice toroidal  transformer inside it.

Here's the box on the shelf in the shack:

Anyhow, PA2OHH, has a really neat on-line grabber for QRSS monitoring on 30M here:

http://www.qsl.net/pa2ohh/grabber.htm

tnx Onno!

And here is a screen grab that I've annotated to aid reading:

So, my Arduino QRSS beacon, which has a p-to-p output of about 4.8V (that's about 60mW- calculated by p-to-p squared / 400) is being decoded in PA2 land (actually in square JO33df) which is about 520km.

I'm lower in frequency than I thought, although I didn't check the frequency after I put the gubbins in the box - so a little tweak up a smidgen and all should be well.

Here's another shot from PA2OHH after I have altered the TX frequency, you can now see my call around 14.0140.135 (ish):

And this one is an image Onno sent to me as a report of my sigs:

As a quick experiment, I decided to test the characteristics of the low pass filter on the output of the QRSS beacon, here's what I find using the tracking generator in the new Spectrum Analyser thingamabob:

So the filter is passing up to 10.something MHz with little or no attenuation and the first harmonic is going to be almost 50dB down - all good!

All in all, not bad, egh?

QRSSing Again

Well,

You may remember way back when I did some mucking about with QRSS (that's really low power slow morse):

http://g0mgx.blogspot.co.uk/2010/12/qrss-beacon.html

I've found another kit from Hans Summers:

www.hanssummers.com

This time it's an Arduino shield - so I can write and fiddle with the software to drive this myself.

Here's the kit as delivered:

it's very simple to make:

and here is the finished thing sat on top of it's Arduino host:

So, a bit of simple software to get the board to send my callsign in FSK QRSS mode, and we now need to align the beacon to be somewhere between 10.140.000 and 10.140.100 - that's quite a narrow band to aim at.

The easiest way seems to be to use the Argo software - it's a kind of spectrum monitoring thingamabob where you can set the offsets associated with the radio connected. So I tuned by FT5000 to 10.139.000 USB (because the carrier offset in USB is 1000Hz) and then entered that as the offset in the Argo software. I then adjusted the beacon to be at what looks like 10.140.060:

I dont really understand why I can see more faded images of the beacon in other parts of the spectrum, but the main beacon seems to be around 10.140.060/065. You can see the end of an "X" and then the start of my call again with a "G" then a "0".

Looking at the output of the beacon on my new Spectrum Analyser thingy, we see this:

The Analyser cant go to an accurate enough frequency, but it confirms that the RF peak is at 10.140 - so I am certainly in the right ballpark and my maths isn't out of bonk.

It looks good and clean on the 'scope too:

Might just take this back with me to A71 land and see what we can see. In the meantime I'll connect this to an antenna and see if anyone can spot me!

Fun, egh?